The present invention relates to a system for the reconstruction of the natural twist between the natural knee and the region of the natural hips in an arrangement between an artificial knee joint and the region of the natural hips after partial resection of the natural condyles of the knee joint and bearing of a part of the femur of the artificial knee joint of a certain size on the resection surfaces of the femur bone, as is described in the applicant""s not previously published German patent application 197 16 300.9-35.
By twist is understood a rotation of the femur bone into itself, which can lead to an angle, which is individually different for every person, between the knee joint on the one hand, and the neck of the thigh and hip head, on the other hand, which decisively influences running behavior and animation.
Should the replacement of the natural knee joint by an artificial total replacement implant now prove to be necessary, for example as a result of a tumor infection, the natural joint parts must be partially resected and replaced by implant components. If the femoral resection is performed in a traditional manner, it can be the case that the femoral components of the artificial knee joint stand at an angle to the hip region that is changed from the angle of the natural knee joint prior to the resection, i.e., as a result, that the natural twist is no longer found in the overall system of the femur after the operation. A changed running behavior and a changed animation of the patient is the direct result.
Before a femur part can be applied on the femur, generally a horizontal bearing surface is first made by resection of the sliding part of the condyles using an appropriate saw. After that, the ventral and dorsal sections as well as the two diagonal sections which connect them to the horizontal bearing surface are also missing.
A device for fixing resection surfaces on the femur and on the tibia for preparation of an implantation of a knee joint total endoprosthesis is known from German patent DE 44 23 717. In this patent, the main point focuses on the ventral section and dorsal section on the femur being made exactly parallel to the frontal resection surface on the tibia. This patent does not give any indication with regard to a possible rotational angle in the production of the resection surfaces, so that when the device disclosed in this patent is handled improperly, the twist after the operation is completely different from the previous one. However, this cannot be readily corrected, particularly since at least one additional serious operation would be necessary.
With the described system, one proceeds such that the frontal section on the tibia is carried out horizontally. The horizontal plane is then shifted in parallel, for example through a parallel plane according to German patent DE 44 23 717, and reproduced on the femoral bone, so that the front femoral resection cut also lies horizontally.
It is proposed that the system have a nail jig with an exactly cuboid (i.e., rectangular parallelepiped in shape) bearing block, which has on its end face seen ventrally a leg projecting therefrom pointing toward the femur, which holds on its end a femur contact feeler in the form of a bolt standing perpendicular to the leg for ventrally lying point support on the femur, and has on its face seen dorsally at least one striking plate projecting therefrom and pointing toward the femur for respective dorsally lying point support on both dorsal condyle rounds (i.e., the femoral part of the knee joint), wherein the bearing block has drill hole pairs passing through it. The arrangement of the drill holes represents the respective size of the femur part, through which fixing nails can be inserted, which secure the bearing block in its position on the femur, and whereby the bearing block can be pulled away from the femur while leaving the fixing nails behind. The system also has a saw jig with an identical basic shape as the bearing block of the nail jig and with an identical arrangement of drill hole pairs in the bearing block, which can be set on the fixing nails so that its face sides define the remaining resection planes.
The connecting components between the nail jig and the saw jig are accordingly the fixing nails, which fit in drill hole pairs both in the bearing block and in the saw jigxe2x80x94depending on the size of the joint, so that the position of the nail jig is converted to the position of the saw jig on the femur stump. Prerequisite for the application of the system is first the production of a horizontal bearing surface for the femur part of the artificial hip joint. The sliding parts of the natural condyles are thereby removed. In approximately 90% of operation cases, the dorsal condyle rounds remain undamaged and can thus be used as a reference point for the determination of the twist. The starting point for consideration in the system is that first a stable three-point bearing is in a position to form a stable system for reproducing the twist. Two of the three points are specified by the dorsally lying contact points of the above-mentioned striking plate on the two condyle rounds.
The still missing third point for the three-point bearing of the nail jig is determined by the femur contact feeler, which takes care of a point-shaped contact with the femur on the opposite side, i.e., ventrally located.
The surgeon must nextxe2x80x94after the size of the femur part to be implanted has been clearly determinedxe2x80x94produce the horizontal bearing surface on the femur, and then set the nail jig on the femur stump in such a way that a stable three-point bearing of the nail jig occurs on the femur stump by virtue of the femur contact feeler and the at least one striking plate for the two condyle rounds.
After producing the stable three-point bearing of the nail jig, the surgeon fixes it onto the horizontal bearing surface using two fixing nails, which he strikes through the pair of drill holes corresponding to the size of the implant and through the bearing block into the femur bone. After that, the nail jig is pulled away from the femur leaving behind the fixing nails, and the above-mentioned saw jig is set on the fixing nails still sticking in the femur. The reproduction of the twist is accomplished based on the identical basic shape of the saw jig as the nail jig and the identical arrangement of the drill hole pairs in the saw jig as in the nail jig. After setting the saw jig on the fixing nails and, if necessary, an additional affixing of the saw jig, the remaining resection sections are then carried out according to the specification of the saw jig. In particular, this involves the dorsal section, the ventral section and the two diagonal sections, such that the thus-produced diagonal section surface connects the horizontal bearing surface with the dorsal or ventral resection surface. Thus, the femur part of the artificial hip joint can be affixed: to the corresponding bearing surfaces on the femur, with or without bone cement.
A typical femur part for an artificial hip joint having corresponding bearing surfaces is likewise shown in German published patent application DE-A-41 41 757.
There is also another starting point for the present invention:
Fundamentally, the system of German patent application 197 16 300.9-35 is based on the reference of the frontal horizontal section on the tibia as well as of the bearing point of a striking plate on the rear condyle rounds of the femur.
Added to this is the fact that;the lateral condyle of the femur lies higher than the medial condyle. The hypothetical connection line from lateral to medial between the two condyles thus slopes relative to the horizontal. This leads to the consideration that the resection surface on the tibia should also be a surface sloping relative to the horizontal, in order to generate as natural conditions as possible in the artificial knee joint. Of course, the question then arises of how the described system can still be used, since this proceeds from the assumption of horizontal sections.